Sheet for multilayer optical recording medium and multilayer optical recording medium using the same

ABSTRACT

Disclosed is a sheet for producing a multilayer optical recording medium having a repeating structure wherein a plurality of optical recording layers are laminated. The sheet for a multilayer optical recording medium has a structure having a unit wherein an optical recording layer and an adhesive layer are laminated, or a structure having a unit wherein an optical recording layer, a barrier layer and an adhesive layer are laminated in this order. The maximum height roughness (Rz) of the optical recording layer or the barrier layer is not more than 500 nm. A multilayer optical recording medium is produced by using the sheet for a multilayer optical recording medium. Also disclosed is a sheet for producing, with high precision, a high-quality multilayer optical recording medium having a repeating unit wherein a plurality of optical recording layers containing a multiphoton absorbing material are laminated. A multilayer optical recording medium is also produced by using this sheet.

This application is the United States national phase application ofInternational Application PCT/JP2009/061267 filed Jun. 15, 2009.

TECHNICAL FIELD

The present invention relates to a sheet for a multilayer opticalrecording medium and a multilayer optical recording medium using thesame. More particularly, the present invention relates to a sheet forproducing a multilayer optical recording medium having a repeatingstructure in which a plurality of optical recording layers are laminatedwith excellent precision and quality, and a multilayer optical recordingmedium produced by using the sheet.

BACKGROUND ART

Recently, multilayer optical recording media utilizing two-photonabsorbing materials are proposed to increase the density of recordedinformation in the optical recording media. To decrease crosstalk in themultilayer optical recording media, a structure in which a non-recordinglayer is disposed between recording layers is proposed (for example,refer to Patent References 1 and 2). However, the multilayer opticalrecording media having the laminate structure described above are, ingeneral, obtained by forming and laminating each layer by the spincoating process, and a problem arises in that maintaining the precisionof the thickness of the film is difficult since the error of thethickness increases as the lamination is repeated.

As a method for overcoming the problem, for example, a process in whicha sheet of a thin film of a non-recording recording layer constitutedwith a pressure sensitive adhesive is attached to a substrate plate, arecording layer having a smaller thickness is formed on thenon-recording layer by a coating process such as a spin coating processor a knife coating process, and these procedures are repeated to formthe desired number of laminated layers, may be conducted. In this case,in general, a barrier layer is formed between the pressure sensitiveadhesive layer and the optical recording layer since resistance of thepressure sensitive adhesive to solvents is poor. The two-photonabsorbing material used for the recording layer is frequently a lowmolecular compound, and the strength of a sheet is insufficient when thesheet is formed from the material. To overcome this problem, in general,a binder polymer exhibiting poor two-photon absorbing property is mixedas the matrix. However, this method decreases the recording sensitivityas the recording layer.

As another process, a process in which a sheet of a thin film of arecording layer constituted with a two-photon absorbing material and asheet of a thin film of a non-recording layer constituted with apressure sensitive adhesive are laminated, is proposed (for example,refer to Patent Reference 3). In accordance with the process using theabove sheet, several layers can be laminated to the substrate plate in asingle step by preparing a unit in which several sheets of a thin filmof a recording layer and several sheets of a thin film of a nonrecording layer are laminated, and production of a multilayer opticalrecording medium can be facilitated.

[Patent Reference 1] Japanese Patent Application Laid-Open No. Heisei11(1999)-250496

[Patent Reference 2] Japanese Patent Application Laid-Open No.2000-67464

[Patent Reference 3] Japanese Patent Application Laid-Open No.2005-209328

DISCLOSURE OF THE INVENTION

[Problems to be Overcome by the Invention]

The processes described in Patent Reference 3 has a problem in that theroughness of the process film is transferred to the extremely thinrecording layer or the barrier layer for forming an extremely thinrecording layer having a thickness as small as 10 to 5,000 nm, andscattering of light takes place due to the roughness although themultilayer optical recording medium can be prepared easily. Since afiller such as silica is added to commercial films such as polyethyleneterephthalate films to prevent blocking or the like, the roughness ofthe process film is transferred to the recording layer or the barrierlayer and it is difficult that scattering of light is prevented as longas the film described above is used as the process film. When a processfilm is coated with a coating fluid containing a material for forming arecording layer or a material for forming a barrier layer used forforming the recording layer, problems arises in that separation of therecording layer or the barrier layer from the process film becomedifficult since a portion of the material migrates into the process filmand that, when the material forming the recording layer is a mixture,some components selectively migrate into the process film and, as aresult, the composition of the obtained recording layer is differentfrom the prescribed composition.

The present invention has been made under the above circumstance and hasan object of providing a sheet for producing a multilayer opticalrecording medium having a repeating structure, in which a plurality ofoptical recording layers comprising the multiphoton absorbing materialare laminated, with excellent precision and quality, and a multilayeroptical recording medium produced by using the sheet.

[Means for Overcoming the Problems]

As the result of intensive studies by the present inventors to achievethe above object, it was found the object could be achieved by using asheet which had a structure comprising a unit in which an opticalrecording layer and an adhesive layer were laminated or a structurecomprising a unit in which an optical recording layer, a barrier layerand an adhesive layer were laminated in this order and had the maximumheight roughness (Rz) of the optical recording layer or the barrierlayer limited to a specific value or smaller. The present invention hasbeen completed based on the knowledge.

The present invention provides:

[1] A sheet for a multilayer optical recording medium having a repeatingstructure comprising a plurality of laminated optical recording layers,wherein the sheet has a structure comprising a unit in which an opticalrecording layer and an adhesive layer are laminated or a structurecomprising a unit in which an optical recording layer, a barrier layerand an adhesive layer are laminated in this order, and a maximum heightroughness (Rz) of the optical recording layer or the barrier layer is500 nm or smaller;

[2] The sheet for a multilayer optical recording medium according to[1]wherein, in the sheet having a structure comprising a unit in whichan optical recording layer and an adhesive layer are laminated, theoptical recording layer is formed by transfer of an optical recordinglayer formed on a process film on a face at a side for forming theoptical recording layer, the face at the side for forming the opticalrecording layer of the process film having a maximum height roughness(Rz) of 500 nm or smaller;

[3] The sheet for a multilayer optical recording medium according to [1,]wherein, in the sheet having a structure comprising a unit in which anoptical recording layer, a barrier layer and an adhesive layer arelaminated, the barrier layer is formed by transfer of a barrier layerformed on a process film on a face at a side for forming the barrierlayer, the face at the side for forming the barrier layer of the processfilm having a maximum height roughness (Rz) of 500 nm or smaller;

[4] The sheet for a multilayer optical recording medium according to anyone of [2] and [3, ]wherein surface film Young's modulus on the face ofthe process film at the side for forming the optical recording layer orat the side for forming the barrier layer is 1.0 GPa or greater;

[5] The sheet for a multilayer optical recording medium according to anyone of [2] to [4, ]wherein the face of the process film at the side forforming the optical recording layer or at the side for forming thebarrier layer comprises no fillers;

[6] The sheet for a multilayer optical recording medium according to anyone of [2] to [5, ]wherein the process film comprises a substrate filmand a coating film disposed on the substrate film, and the coating filmhas a thickness of 80 to 10,000 nm and is disposed on the face of theprocess film at the side for forming the optical recording layer or atthe side for forming the barrier layer to suppress roughness of thesubstrate;

[7] The sheet for a multilayer optical recording medium according to anyone of [2] to [6, ]wherein the face of the process film at the side forforming the optical recording layer or at the side for forming thebarrier layer comprises a coating film comprising a polyester-basedresin or a resin cured with an active energy ray;

[8] The sheet for a multilayer optical recording medium according to anyone of [1] to [7, ]wherein the optical recording layer is a layercomprising a multiphoton absorbing material;

[9] A multilayer optical recording medium prepared by using the sheetaccording to any one of [1] to [8]; and

[10] A film for producing the sheet for a multilayer optical recordingmedium according to any one of [1] to [9, ]wherein an optical recordinglayer or a barrier layer is formed on a process film on a face at a sidefor forming the optical recording layer or at a side for forming thebarrier layer, the face at the side for forming the optical recordinglayer or at the side for forming the barrier layer of the process filmhaving a maximum height roughness (Rz) of 500 nm or smaller.

THE EFFECT OF THE INVENTION

In accordance with the present invention, a sheet for producing amultilayer optical recording medium having a repeating structure inwhich a plurality of optical recording layers are laminated withexcellent precision and quality and a multilayer optical recordingmedium produced by using the sheet can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagram exhibiting the structure of an example of a layerof a pressure sensitive adhesive having release films on both faces.

FIG. 2 shows a diagram exhibiting the structure of an example of theoptical recording layer having a process film.

FIG. 3 shows a diagram exhibiting an example of Unit A in which aprocess film and a release film are laminated.

FIG. 4 shows a diagram exhibiting the structure of an example of Sheet Aof the present invention having two layers of Unit A in which an opticalrecording layer and a pressure sensitive adhesive layer are laminated.

FIG. 5 shows a diagram exhibiting an example of the barrier layer havinga process film.

FIG. 6 shows a diagram exhibiting an example of the laminate forproducing Sheet B of the present invention.

FIG. 7 shows a diagram exhibiting the structure of an example of Sheet Bof the present invention.

FIG. 8 shows a diagram exhibiting a sectional view of an example of thestructure of the multilayer optical recording medium of the presentinvention.

FIG. 9 shows a diagram exhibiting a sectional view of another example ofthe structure of the multilayer optical recording medium of the presentinvention.

In the Figures, reference numerals mean as follows: 1, 1-1, 1-2,1-(n-1), 1-n and 11: adhesive layers (pressure sensitive adhesivelayers); 2: the first release film; 3: the second release film; 4, 4-1,4-2, 4-(n-1) and 4-n: optical recording layers; 4 a, 4 a-1, 4 a-2, 4a-(n-1) and 4 a-n: optical recording layers; 5: a process film; 6, 6-1,6-2, 6-(n-1) and 6-n: Unit A; 7, 7-1, 7-2, 7-(n-1) and 7-n: barrierlayers; 8, 8-1, 8-2, 8-(n-1) and 8-n: Unit B; 9: a substrate plate; 10:a pressure sensitive adhesive layer having release films on both faces;12: a transparent protective film; 20: an optical recording layer havinga process film; 30: Unit A having a process film and a release film; 40:Sheet A; 50: a barrier layer having a process film; 60: a laminate; 70:Sheet B; and 80 and 90: multilayer optical recording layers.

THE MOST PREFERRED EMBODIMENT TO CARRY OUT THE INVENTION

The sheet for a multilayer optical recording medium of the presentinvention will be described in the following.

[Sheet for a Multilayer Optical Recording Medium]

The sheet for a multilayer optical recording medium (hereinafter,referred to simply as “the sheet”, occasionally) is a sheet for amultilayer optical recording medium having a repeating structurecomprising a plurality of laminated optical recording layers, which ischaracterized in that the sheet has a structure comprising a unit inwhich an optical recording layer and an adhesive layer are laminated ora structure in which an optical recording layer, a barrier layer and anadhesive layer are laminated in this order, wherein the maximum heightof roughness (Rz) of the optical recording layer or the barrier layer is500 nm or smaller.

(Optical Recording Layer)

In the sheet of the present invention, the material constituting theoptical recording layer is not particularly limited, and a suitablematerial can be selected as desired from conventional materials known asthe materials constituting optical recording layers in optical recordingmedia. It is preferable that the material comprises a multiphotonabsorbing material having an absorption at 200 to 800 nm. Themultiphoton absorbing material means a compound having the property suchthat the compound absorbs at least two photons simultaneously and isconverted into an excited state. From the standpoint of obtaining thepractically sufficient recording density, materials comprising amaterial absorbing two photons which has a sectional area of two photonabsorption of 0.1 GM or greater are preferable, and materials comprisinga material absorbing two photons which has a sectional area of twophoton absorption of 100 GM or greater are more preferable among thematerials exhibiting the above property. The material described abovemay be, for example, a material constituted with the multiphotonabsorbing material alone, a material constituted with the multiphotonabsorbing material and other reactive compounds which are changed by theenergy transfer from the excited multiphoton absorbing material or amaterial obtained by mixing the above compounds into a matrix. “GM”described above means 10⁻⁵⁰ cm⁴-s-molecule⁻¹-photon⁻¹.

Although the material constituting the matrix described above may be aninorganic material or an organic material, an organic macro-molecularmaterial is preferable since production of the sheet of the presentinvention is facilitated and the material can be selected from varietyof materials. The macromolecular material may be a homopolymer or acopolymer. The type of the monomer, the molecular weight and the form ofpolymerization are not particularly limited.

<Macromolecular Material>

Examples of the macromolecular material described above include varioustypes of polyolefins such as various types of polyethylene,ethylene/1-butene copolymers, ethylene/4-methyl-1-pentene copolymers,ethylene/1-hexene copolymers, polypropylene, ethylene/propylenecopolymers, propylene/1-butene copolymers, poly1-butene,1-butene/4-methyl-1-pentene copolymers, poly4-methyl-1-pentene,poly3-methyl-1-butene, ethylene/cyclic olefin copolymers and cyclicolefin-based resins; ethylene/vinyl acetate copolymers;poly(meth)acrylates such as ethylene/acrylic acid copolymers, metalsalts of ethylene/acrylic acid copolymers, polymethyl methacrylate andalicyclic acrylic resins; polyester-based resins such as polyethyleneterephthalate and polyethylene naphthalate; fluororesins such aspolyperfluoroethylene and perfluoroalkenyl vinyl ether polymers;polystyrenes; polyvinyl alcohol; polycarbonates; polyphenylene sulfide;polyether sulfone; polyimides; polyphenylene oxide; olefin/N-substitutedmaleimide copolymers; allyl carbonate resins; epoxy acrylate resins; andurethane acrylate resins. The macromolecular material may be used singlyor in combination of two or more.

<Multiphoton Absorbing Material>

The multiphoton absorbing material may be a multiphoton absorbingmaterial alone, a material comprising a multiphoton absorbing componentchemically bonded to the matrix as a component of the main chain or sidechains or a multiphoton absorbing material simply dispersed or dissolvedin the matrix. The multiphoton absorbing material is not particularlylimited, and various compounds can be used. Examples of the multiphotonabsorbing material include compounds such as cyanine-based compounds,styryl-based compounds, pyrilium-based compounds, thiapyrilium-basedcompounds, melocyanine-based compounds, arylidene-based compounds,oxonol-based compounds, squalium-based compounds, azulenium-basedcompounds, coumarine-based compounds, pyran-based compounds,quinone-based compounds, anthraquinone-based compounds,triphenylmethane-based compounds, diphenylmethane-based compounds,xanthene-based compounds, thioxanthene-based compounds,phenothiazine-based compounds, azo-based compounds, azomethine-basedcompounds, fluorenone-based compounds, diarylethene-based compounds,spiropyran-based compounds, fulguide-based compounds, perylene-basedcompounds, polyene-based compounds, diphenylamine-based compounds,quinacridone-based compounds, azulenium-based compounds, porphyrin-basedcompounds, phthalocyanine-based compounds, styrene-based compounds,phenylenevinylene-based compounds, triphenylamine-based compounds andcarbazole-based compounds.

In the present invention, the molecular weight of the multiphotonabsorbing material is not particularly limited. From the standpoint ofsuppressing migration into the process film, it is preferable that themolecular weight is 300 or greater as the number-average molecularweight (Mn). The upper limit of the molecular weight is not particularlylimited. The upper limit of the molecular weight is, in general, about100,000 as the number-average molecular weight. As the multiphotonabsorbing material, two-photon absorbing materials are preferable.

The macromolecular multiphoton absorbing material can be obtained bychemically bonding the multiphoton absorbing component to the matrixdescribed above as a component of the main chain or the side chains.

The number-average molecular weight described above is the valueobtained by the measurement by the gel permeation chromatography (GPC)and expressed as the value of the corresponding polystyrene.

Examples of the method of recording using the multiphoton absorbingmaterial include a method in which modulation in the refractive index isread using a material isomerized with light such as compounds having azogroup, C═C group or C═N group, a material polymerized with light such as(meth)acrylate compounds, a material having a structure reversiblychanging with light such as organic photochromic materials or an organicrefractive material forming charge distribution with light; a method inwhich fluorescent light is read using a material having the fluorescentproperty changing with light; and a method in which modulation ofabsorption or modulation of refractive index is read using a combinationof a material generating an acid with light and a coloring agentdeveloping color with an acid or a combination of an agent erasing colorand a coloring agent which allows erasure of the color. In the aboverecording methods, the multiphoton absorbing compound itself may havethe photoreactivity described above or the reaction may be induced byenergy transfer from the multiphoton absorbing compound excited bymultiphoton absorption to another reactive material.

<Properties of Optical Recording Layer>

In the sheet of the present invention, the thickness of the opticalrecording layer is not particularly limited. The thickness is, ingeneral, about 0.04 to 50 μm and preferably 0.05 to 10 μm.

It is necessary that the maximum height roughness (Rz) of the opticalrecording layer is 500 nm or smaller. The maximum height roughness (Rz)is the surface roughness expressed by the maximum height (the differencebetween the highest portion and the lowest portion) in the sectionalcurve from which the reference length has been subtracted (described inJapanese Industrial Standard B 0601:2001). The value is varied greatlywhen a locally high portion or a locally low portion is present.Therefore, a great maximum height roughness (Rz) causes deterioration inthe recording properties of the multilayer optical recording medium evenwhen the average roughness of the surface of the optical recording layeror the barrier layer described below is small. When the maximum heightroughness (Rz) of the optical recording layer and the barrier layer iskept at 500 nm or smaller, local scattering of light is suppressed, andthe multilayer optical recording medium exhibiting the excellentrecording properties can be obtained. When Rz exceeds 500 nm, a drawbackarises in that scattering of light takes place in the obtained opticalrecording medium. It is preferable that Rz is 300 nm or smaller and morepreferably 100 nm or smaller. The lower limit of Rz is not particularlylimited. It is difficult that an optical recording layer having a valueof Rz smaller than 0.1 nm is formed. Therefore, the lower limit of Rzis, in general, about 0.1 nm.

In the sheet of the present invention, the formation of the opticalrecording layer having the value of Rz described above can be conductedby transferring an optical recording layer formed on the face having avalue of Rz of 500 nm or smaller of a process film at the side forforming the optical recording layer to the pressure sensitive adhesivelayer as described later. The face of a process film at the side forforming the optical recording layer will be referred to as “the opticalrecording layer forming face” hereinafter.

The method of measurement of Rz described above will be described below.

(Adhesive Layer)

The adhesive constituting the adhesive layer in the sheet of the presentinvention is not particularly limited. Pressure sensitive adhesivesexhibiting the pressure sensitive adhesive property at the ordinarytemperature are preferable, and acrylic pressure sensitive adhesives aremore preferable due to the excellent transparency.

As the acrylic pressure sensitive adhesive, for example, pressuresensitive adhesives comprising a (meth)acrylic acid ester-basedcopolymer and a crosslinking agent can be used.

<(Meth)acrylic Acid Ester-Based Copolymer>

As the (meth)acrylic acid ester-based copolymer, copolymers of a(meth)acrylic acid ester in which the alkyl group in the ester portionhas 1 to 20 carbon atoms with a monomer having a functional group havingactive hydrogen and other monomers which are used where desired arepreferable.

Examples of the (meth)acrylic acid esters in which the alkyl group inthe ester portion has 1 to 20 carbon atoms include methyl(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl(meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth) acrylate,t-butyl (meth) acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate,cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl(meth)acrylate, decyl (meth)acrylate, dodecyl (meth)acrylate, myristyl(meth)acrylate, palmityl (meth)acrylate and stearyl (meth)acrylate. Theabove (meth)acrylic acid ester may be used singly or in combination oftwo or more.

Examples of the monomer having a functional group having active hydrogeninclude hydroxyalkyl (meth)acrylates such as 2-hydroxyethyl(meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl(meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl(meth)acrylate and 4-hydroxybutyl (meth)acrylate; monoalkylaminoalkyl(meth)acrylates such as monomethylaminoethyl (meth)acrylate,monoethylaminoethyl (meth) acrylate, monomethylaminopropyl(meth)acrylate and monoethylaminopropyl (meth)acrylate; andethylenically unsaturated carboxylic acids such as acrylic acid,methacrylic acid, crotonic acid, maleic acid, itaconic acid andcitraconic acid. The above monomer may be used singly or in combinationof two or more.

Examples of the other monomer which is used where desired include vinylesters such as vinyl acetate and vinyl propionate; olefins such asethylene, propylene and isobutylene; halogenated olefins such as vinylchloride and vinylidene chloride; styrene-based monomers such as styreneand α-methylstyrene; diene-based monomers such as butadiene, isopreneand chloroprene; nitrile-based monomers such as acrylonitrile andmethacrylonitrile; and acrylamides such as acrylamide,N-methyl-acrylamide and N,N-dimethylacrylamide. The above monomer may beused singly or in combination of two or more.

The form of copolymerization of the (meth)acrylic acid ester-basedcopolymer is not particularly limited and may be any of a randomcopolymer, a block copolymer and a graft copolymer. It is preferablethat the molecular weight is in the range of 300,000 to 2,000,000 as theweight-average molecular weight.

The weight-average molecular weight described above is the valueobtained by the measurement by the gel permeation chromatography (GPC)and expressed as the value of the corresponding polystyrene.

In the present invention, the (meth)acrylic acid ester-based copolymermay be used singly or in combination of two or more.

<Crosslinking Agent>

The crosslinking agent in the acrylic pressure sensitive adhesive is notparticularly limited, and a crosslinking agent can be suitably selectedas desired from conventional crosslinking agents used for acrylicpressure sensitive adhesives. Examples of the crosslinking agent includepolyisocyanate compounds, epoxy compounds, aziridine-based compounds,melamine resins, urea resins, dialdehydes, methylol polymers, metalchelate compounds, metal alkoxides and metal salts. Among thesecrosslinking agents, alicyclic polyisocyanate-based compounds, aliphaticpolyisocyanate-based compounds, alicyclic epoxy-based compounds,aliphatic epoxy-based compounds, metal chelate compounds and aliphaticaziridine-based compounds are preferable since change in thetransmittance of light due to change in the color (yellowing) of thelayer of a pressure sensitive adhesive is suppressed, and degradationdue to irradiation with laser is suppressed.

The metal chelate compound is not particularly limited, and a suitablecompound can be selected from compounds conventionally used as the metalchelate compound in acrylic pressure sensitive adhesives. Examples ofthe metal chelate compound include chelate compounds in which the metalatom is aluminum, zirconium, titanium, zinc, iron or tin.

Examples of the alicyclic polyisocyanate-based compound and thealiphatic polyisocyanate-based compound include isophorone diisocyanate,bicycloheptane triisocyanate, cyclopentylene diisocyanate, cyclohexylenediisocyanate, methylcyclohexylene diisocyanate, hydrogenateddiphenylmethane diisocyanate, hexamethylene diisocyanate,trimethyl-hexamethylene diisocyanate, lysine diisocyanate, biuretcompounds and isocyanurate compounds based on these polyisocyanates, andadducts as the reaction products with low molecular weight compoundshaving active hydrogen such as ethylene glycol, propylene glycol,neopentyl glycol, trimethylolpropane and castor oil.

Examples of the alicyclic epoxy-based compound and the aliphaticepoxy-based compound include 3,4-epoxycyclohexylmethyl3,4-epoxycyclohexylcarboxylate,1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, hydrogenated bisphenol Adiglycidyl ether, polyethylene glycol diglycidyl ether, polypropyleneglycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, adipic acidglycidyl ester and sebacic acid glycidyl ester.

Examples of the aluminum chelate compound include diisopropoxyaluminummonooleyl acetoacetate, monoisopropoxyaluminum bisoleyl acetoacetate,monoisopropoxyaluminum monooleate monoethyl acetoacetate,diisopropoxyaluminum monolauryl acetoacetate, diisopropoxyaluminummonostearyl acetoacetate, diisopropoxyaluminum monoisostearylacetoacetate, monoisopropoxyaluminum mono-N-lauroyl-β-alanate monolaurylacetoacetate, aluminum trisacetylacetonate, monoacetylacetonatoaluminumbis(isobutyl acetoacetate) chelate, monoacetylacetonatoaluminumbis(2-ethylhexyl acetoacetate) chelate, monoacetylacetonatoaluminumbis(dodecyl acetoacetate) chelate and monoacetylacetonatoaluminubis(oleyl acetoacetate) chelate.

The aliphatic aziridine compound is not particularly limited, and asuitable compound can be selected as desired from compoundsconventionally used as the aliphatic aziridine-based compound in acrylicpressure sensitive adhesives. Examples of the aliphatic aziridine-basedcompound include trimethylolpropane tri(2-methyl-1-aziridinepropionate),tetramethylolmethane tri-β-aziridinylpropionate,2,2′-bishydroxymethyl-butanol tris[3-(1-aziridinyl)propionate] and1,6-hexamethylenediethyleneurea.

In the present invention, the alicyclic polyisocyanate-based compound,the aliphatic polyisocyanate-based compound, the alicyclic epoxy-basedcompound, the aliphatic epoxy-based compound, the metal chelate compoundand the aziridine-based compound which are described above may be usedsingly or in combination of two or more. The content is selected, ingeneral, in the range of 0.01 to 5.0 parts by mass, preferably in therange of 0.05 to 3.0 parts by mass and more preferably in the range of0.1 to 1.0 part by mass based on 100 parts by mass of the (meth)acrylicacid ester-based copolymer described above from the standpoint of theproperties as the pressure sensitive adhesive.

To the pressure sensitive adhesive, tackifiers, antioxidants,ultraviolet light absorbers, light stabilizers, softeners and fillersmay be added where desired as long as the effect of the presentinvention is not adversely affected.

The thickness of the pressure sensitive adhesive layer in the sheet ofthe present invention is not particularly limited. The thickness is, ingeneral, about 1 to 100 μm and preferably 2 to 30 μm.

The method of forming the adhesive layer will be described below.

(Barrier Layer)

The barrier layer in the sheet of the present invention is the layerdisposed on the surface of the pressure sensitive adhesive layerdescribed above where desired so that the optical recording layer isformed on the pressure sensitive adhesive layer using the material forforming the optical recording layer comprising a solvent by the spincoating process or the like exhibiting excellent productivity. When theoptical recording layer is formed directly on the pressure sensitiveadhesive layer by the spin coating process or the like without disposingthe barrier layer, the pressure sensitive layer may be invaded with thesolvent in the material for forming the optical recording layer or thematerial for forming the non-recording layer may be mixed into thepressure sensitive adhesive layer due to the poor resistance to solventof the pressure resistive adhesive layer. Thus, the obtained multilayeroptical recording medium exhibits poor precision and poor quality.

Examples of the material constituting the barrier layer include thevarious macromolecular materials described as the examples of thematerial constituting the matrix in the description of the opticalrecording layer. The material constituting the barrier layer may be usedsingly or in combination of two or more. Among the above materials,polyvinyl alcohol is preferable. Since polyvinyl alcohol is soluble inwater and can be applied in the form of an aqueous solution and dried toform the barrier layer, polyvinyl alcohol is advantageous from thestandpoint of the workability.

<Properties of Harrier Layer>

In the sheet of the present invention, the thickness of the barrierlayer is not particularly limited. The thickness is, in general, about0.01 to 100 μm and preferably 0.05 to 30 μm.

It is necessary that the maximum height roughness (Rz) of the barrierlayer is 500 nm or smaller. When Rz exceeds 500 nm, the opticalrecording layer formed on the harrier layer by the spin coating processor the like has the same value of Rz, and a drawback arises in thatscattering of light takes place in the obtained optical recordingmedium.

It is preferable that Rz is 300 nm or smaller and more preferably 100 nmor smaller. The lower limit of Rz is not particularly specified, and asmaller value is more preferable. However, it is difficult that abarrier layer having a value of Rz smaller than 0.1 nm is formed, andthe lower limit of Rz is, in general, about 0.1 nm.

In the sheet of the present invention, the formation of the barrierlayer having the value of Rz described above can be conducted bytransferring a barrier layer formed on the face having a value of Rz of500 nm or smaller of a process film at the side for forming the barrierlayer to the pressure sensitive adhesive layer as described later. Theface of a process film at the side for forming the barrier layer will bereferred to as “the face for forming the barrier layer” hereinafter.

As the method of forming the optical recording layer on the barrierlayer formed as described above, the process of applying the materialfor forming the optical recording layer by the spin coating process ispreferable. By using the spin coating process, a coating fluidcontaining the multiphoton absorbing material alone without containingbinders can be used as the material for forming the optical recordinglayer, and the optical recording layer exhibiting excellent recordingsensitivity can be formed.

The method of measurement of Rz of the barrier layer will be describedbelow.

(Preparation of the Sheet for a Multilayer Optical Recording Medium)

The sheet for a multilayer optical recording medium of the presentinvention includes two embodiments as described above, i.e., (1) thesheet comprising a unit (Unit A) in which an optical recording layer andan adhesive layer are laminated (hereinafter, referred to as Sheet A)and (2) the sheet comprising a unit (Unit B) in which an opticalrecording layer, a barrier layer and an adhesive layer are laminated inthis order (hereinafter, referred to as Sheet B).

<Preparation of Sheet A>

As the process for preparing Sheet A in the present invention, forexample, the process described in the following can be conducted.

As the first step, a pressure sensitive adhesive layer having releasefilms on both faces is prepared. FIG. 1 shows a diagram exhibiting thestructure of an example of a layer of a pressure sensitive adhesivehaving release films on both faces. The pressure sensitive adhesivelayer having release films on both faces 10 has a structure such that apressure sensitive adhesive layer 1 is disposed between the firstrelease film 2 and the second release film 3.

The pressure sensitive adhesive layer having release films on both faces10 can be prepared, for example, by coating the face treated forreleasing of the first release film 2 with the pressure sensitiveadhesive described above by a conventional process such as the knifecoating process, the roll coating process, the bar coating process, theblade coating process, the die coating process and gravure coatingprocess in an amount such that a layer having a prescribed thickness isformed, followed by drying the formed coating layer and laminating thesecond release film 3 on the formed pressure sensitive adhesive layer 1.

As the release film described above, a release film conventionally usedfor a pressure sensitive adhesive layer may be used.

The release film described above is not particularly limited. Examplesof the release film include films obtained by coating a polyolefin filmsuch as a polyethylene film and a polypropylene film or a polyester filmsuch as a polyethylene terephthalate film with a releasing agent such asa silicone resin to form a layer of a releasing agent. The thickness ofthe release film is, in general, about 20 to 150 μm although thethickness is not particularly limited.

Since it is preferable that the maximum height roughness (Rz) of thesurface of the pressure sensitive adhesive layer is smaller, it ispreferable that Rz of the face of the release film treated for releasingis 500 nm or smaller.

Separately, an optical recording layer having a process film is preparedas the film for producing the sheet for multilayer optical recordingmedium described below. FIG. 2 shows a diagram exhibiting the structureof an example of the optical recording layer having a process film. Theoptical recording layer having a process film 20 has a structure suchthat an optical recording layer 4 is disposed on a process film 5.

The optical recording layer having a process film 20 can be prepared,using a process film in which the maximum height roughness (Rz) of theface for forming the optical recording layer is 500 nm or smaller, bycoating the face for forming the optical recording layer with a coatingfluid comprising a material for forming the optical recording layerwhich comprises a multiphoton absorbing material, preferably atwo-photon absorbing material, and a matrix material such as amacromolecular material in suitable relative amounts by a conventionalprocess such as the knife coating process, the roll coating process, thebar coating process, the blade coating process, the die coating processand gravure coating process in an amount such that a layer having aprescribed thickness is formed, followed by drying the formed coatinglayer to form the optical recording layer 4.

The process film 5 will be described specifically below.

Using the pressure sensitive adhesive layer having release films on bothfaces 10 and the optical recording layer having a process film 20prepared as described above, Unit A in which the optical recording layerand the pressure sensitive adhesive layer are laminated is prepared.FIG. 3 shows a diagram exhibiting an example of the unit having alaminate of an optical recording layer and a pressure sensitive adhesivelayer and disposed between a process film and a release film(hereinafter, referred to as Unit A having a process film and a releasefilm). Unit A having a process film and a release film 30 has astructure such that Unit A 6 in which the optical recording layer 4 andthe pressure sensitive adhesive layer 1 are laminated has a process film5 at the side of the optical recording layer 4 and the first releasefilm 2 at the side of the pressure sensitive adhesive layer 1.

Unit A having a process film and a release film 30 having the structuredescribed above can be prepared, for example, as described in thefollowing.

The second release film 3 in the pressure sensitive adhesive layerhaving release films on both faces 10 prepared as described above ispeeled. The face of the optical recording layer 4 in the opticalrecording layer having a process film 20 prepared as described above islaminated to the exposed pressure sensitive adhesive layer 1, and SheetA comprising Unit A having a process film and a release film can beobtained as described above.

FIG. 4 shows a diagram exhibiting the structure of an example of Sheet Aof the present invention having two layers of Unit A in which an opticalrecording layer and a pressure sensitive adhesive layer are laminated.Sheet A 40 of the present invention can be prepared as described in thefollowing. However the process for preparing Sheet A is not limited tothe process described in the following.

The process film 5 in Unit A 30 having a process film and a release filmobtained as described above is peeled, and the face of the pressuresensitive adhesive layer 1-2 exposed by peeling the second release film3 in the pressure sensitive adhesive layer having release films on bothfaces 10 is laminated to the face of the optical recording layer 4-1exposed above. Then, the first release film 2 is peeled, and the face ofthe optical recording layer 4-2 of the optical recording layer having aprocess film 20 is laminated to the face of the pressure sensitiveadhesive layer 1-2 exposed above, and Unit A 6-2 in which the opticalrecording layer 4-2 and the pressure sensitive adhesive layer 1-2 arelaminated can be formed.

In this manner, Sheet A 40 of the present invention having two laminatedlayers of Unit A, i.e., Unit A 6-1 in which the optical recording layer4-1 and the pressure sensitive adhesive layer 1-1 are laminated and UnitA 6-2 in which the optical recording layer 4-2 and the pressuresensitive adhesive layer 1-2 are laminated as shown in FIG. 4, can beprepared. A process film 5 is disposed on the optical recording layer4-2, and the first release film 2 is disposed on the pressure sensitiveadhesive layer 1-1.

The number of Unit A laminated in Sheet A of the present invention is,in general, about 1 to 6.

<Preparation of Sheet B>

As the process for preparing Sheet B of the present invention, forexample, the process described in the following can be conducted.

As the first step, the pressure sensitive adhesive layer having releasefilms on both faces shown in FIG. 1 is prepared by the process similarto the process for preparing Sheet A described above. Separately, abarrier layer having a process film is prepared as the film forproducing the sheet for multilayer optical recording medium describedbelow.

FIG. 5 shows a diagram exhibiting an example of the barrier layer havinga process film. The barrier layer having a process film 50 has astructure such that a barrier layer 7 is disposed on a process film 5.

The barrier layer having a process film 50 can be prepared, for example,using a process film 5 in which the face for forming the barrier layerhas a maximum height roughness (Rz) of 500 nm or smaller, by coating theface for forming the barrier layer with a coating fluid comprising thematerial for forming the barrier layer by a conventional process such asthe knife coating process, the roll coating process, the bar coatingprocess, the blade coating process, the die coating process and thegravure coating process in an amount such that a layer having aprescribed thickness is formed, followed by drying the formed coatinglayer to form the barrier layer 7.

The process film 5 will be described specifically below.

Then, the second release film 3 in the pressure sensitive adhesive layerhaving release films on both faces 10 shown in FIG. 1 is peeled, and theface of the barrier layer 7 in the barrier layer having a process film50 prepared as described above is laminated to the exposed pressuresensitive adhesive layer 1. After the process film 5 is peeled, theexposed barrier layer 7 is coated with a coating fluid comprising amultiphoton absorbing material, preferably a two-photon absorbingmaterial, by a conventional process such as the spin coating process,the knife coating process, the roll coating process, the bar coatingprocess, the blade coating process, the die coating process, the gravurecoating process and the capillary coating process in an amount such thata layer having a prescribed thickness is formed, followed by drying theformed coating layer to form the optical recording layer. Thus, thelaminate 60 having Sheet B disposed on the first release film 2 as shownin FIG. 6 can be obtained, wherein Sheet B comprises Unit B 8 in whichthe optical recording layer 4 a, the barrier layer 7 and the pressuresensitive adhesive layer 1 are laminated in this order.

When the optical recording layer is formed directly on the barrier layerby the spin coating process or the like as described above, it is madepossible that the coating fluid comprising the multiphoton absorbingmaterial alone is used without using a matrix material such as amacromolecular material, and the optical recording layer exhibitingexcellent recording sensitivity can be formed.

FIG. 7 shows a diagram exhibiting the structure of an example of Sheet Bof the present invention. Sheet B 70 of the present invention has astructure such that two layers of Unit B, i.e., Unit B 8-1 in which anoptical recording layer 4 a-1, a barrier layer 7-1 and a pressuresensitive adhesive layer 1-1 are laminated in this order and Unit B 8-2in which an optical recording layer 4 a-2, a barrier layer 7-2 and apressure sensitive adhesive layer 1-2 are laminated in this order, aredisposed on the first release film 2.

Sheet B 70 can be prepared, for example, by preparing two sheets of thelaminate 60 shown in FIG. 6, followed by laminating the face of thepressure sensitive adhesive layer 1 exposed by peeling the first releasefilm 2 in the second laminate to the face of the first laminate 4 a.However, the process for preparing Sheet B 70 is not limited to theprocess described above.

The number of Unit B described above laminated in Sheet B of the presentinvention is, in general, about 1 to 6.

(Process Film)

<Properties of the Process Film>

The process film is a film having a structure comprising a substratefilm and a coating film disposed on the surface of the substrate, wheredesired.

The formation of the optical recording layer in Sheet A comprising UnitA in which the optical recording layer and the pressure sensitiveadhesive layer are laminated and the formation of the barrier layer inSheet B comprising Unit B in which the optical recording layer, thebarrier layer and the pressure sensitive adhesive layer are laminated inthis order can be achieved by transferring the optical recording layerand the barrier layer, respectively, formed on the process film to thepressure sensitive adhesive layer,

In the present invention, it is necessary that the maximum heightroughness (Rz) of each of the optical recording layer and the barrierlayer described above is 500 nm or smaller, preferably 300 nm or smallerand more preferably 0.01 to 100 nm based on the reason described above.Therefore, for forming the optical recording layer and the barrier layerhaving Rz described above, it is essential that the maximum heightroughness (Rz) of the face for forming the optical recording layer andthe face for forming the barrier layer, respectively, in the processfilm described above to be 500 nm or smaller, preferably 300 nm orsmaller and more preferably 0.01 to 100 nm similarly to the conditiondescribed above.

When the coating film of the face for forming the optical recordinglayer in the process film is soft, low molecular weight components inthe optical recording layer migrate into the coating film when theoptical recording layer is formed on the surface film. This causesproblems in that the properties for recording change and that separationof the optical recording layer from the process film becomes difficult.

Therefore, in the present invention, it is preferable that the surfacefilm Young's modulus of the process film on the face for forming theoptical recording layer or the face for forming the barrier layer is 1.0GPa or greater and more preferably 1.5 to 15 GPa.

The methods of the measurement of the maximum height roughness (Rz) andthe surface film Young's modulus of the face for forming the opticalrecording layer and the face for forming the barrier layer in theprocess film will be described below.

(Preparation of the Process Film)

The process film exhibits the releasing property so that the opticalrecording layer and the barrier layer formed on the film can beseparated. Although the face for forming the optical recording layer andthe face for forming the barrier layer of the substrate film may betreated for releasing or may have a coating film for suppressingroughness of the substrate film or a coating film for adjusting thesurface film Young's modulus, it is essential that Rz be in the rangedescribed above.

As the releasing treatment, for example, the substrate film can becoated with a conventional releasing agent such as a silicone-basedreleasing agent, a butadiene-based releasing agent and a fluorine-basedreleasing agent. The thickness of the layer of the releasing agent isnot particularly limited and can be set as desired. The thickness is, ingeneral, 0.05 to 50 μm.

It is preferable that the peeling strength of the process film is 10 to700 mN/25 mm. When the peeling strength is in this range, workability oftransfer of the optical recording layer or the barrier layer formed onthe process film is excellent. It is more preferable that the peelingstrength is 30 to 300 mN/25 mm.

For the process film, it is preferable that the face for forming theoptical recording layer or the face for forming the barrier layercomprises no fillers. It is preferable that the roughness of thesubstrate is suppressed by forming a coating film having a thickness ofabout 10 to 10,000 nm, more preferably 50 to 8,000 nm and mostpreferably 80 to 5,000 nm. Suppressing the roughness means decreasingthe value of the surface roughness by forming a coating film. As theindex for the surface roughness, Rz described above can be used.

The coating film for suppressing the roughness is not particularlylimited and may be any of inorganic coating films and organic coatingfilms as long as the optical recording layer or the barrier layer formedon the coating film can be peeled. Coating films of polyester-basedresins such as alkyd resins and coating films of resins cured with anactive energy ray are preferable. The coating films of polyester-basedresins and the coating films of resins cured with an active energy raydo not cause repelling of the coating fluid comprising the material forforming the optical recording layer or the barrier layer of the presentinvention since these films have a suitable surface tension, and theoptical recording layer or the barrier layer having a small maximumheight roughness (Rz) can be easily formed. The formed optical recordinglayer or the barrier layer can be easily peeled. When repelling of thecoating fluid takes place, the repelled portion forms a defect and thevalue of the maximum height roughness (Rz) is increased or,occasionally, the optical recording layer or the barrier layer itselfcannot be formed. In addition, transfer of low molecular weightcomponents such as multiphoton absorbing material to those coating filmsdescribed above is small.

(a) Substrate Film

Examples of the substrate film in the process film include polyesterfilms such as polyethylene terephthalate films, polybutyleneterephthalate films and polyethylene naphthalate films; polyethylenefilms; polypropylene films; polyvinyl chloride films; polyvinylidenechloride films; polyvinyl alcohol films; ethylene-vinyl acetatecopolymer films; polystyrene films; polycarbonate films;polymethylpentene films; polysulfone films; polyether ether ketonefilms; polyether sulfone films; polyphenylene sulfide films; polyetherimide films; polyimide films; fluororesin films; polyamide films;acrylic resin films; norbornene-based resin films; and cycloolefin resinfilms.

The thickness of the substrate film is not particularly limited. Thethickness is, in general, about 1 to 500 μm and preferably 2 to 200 μm.

Where necessary, the face for forming the coating film of the substratefilm may be subjected, for example, to the treatment by coronadischarge, the treatment by plasma discharge, the treatment with chromicacid (a wet process), the treatment with flames, the treatment with theheated air or the treatment with ozone and irradiation with ultravioletlight so that adhesion with the coating film formed on the substratefilm is enhanced.

(b) Formation of a Coating Film of a Polyester-Based Resin

As the coating film of the polyester-based resin, coating films of alkydresins having a crosslinked structure are preferable. As the process forforming the film, for example, the process comprising curing a layercomprising a heat curable resin composition comprising (X) an alkydresin, (Y) a crosslinking agent and, where desired, (Z) a curingcatalyst by heating can be conducted.

The alkyd resin of Component (X) is not particularly limited, and aresin can be suitably selected from resins conventionally known as thealkyd resins. The alkyd resin is a resin obtained by condensation of apolyhydric alcohol and a polybasic acid and includes nonconvertiblealkyd resins which are condensates of dibasic acids and dihydricalcohols or modification products with non drying oils and convertiblealkyd resins which are condensates of dibasic acids and alcohols havinga functionality of three or greater. Any of these alkyd resins can beused in the present invention.

Examples of the crosslinking agent of Component (Y) include amino resinssuch as melamine resins and urea resins, urethane resins, epoxy resinsand phenol resins.

In the present invention, the crosslinking agent of Component (Y) may beused singly or in combination of two or more.

It is preferable that the relative amounts of Component (X) to Component(Y) in the heat curable resin composition is in the range of 70:30 to10:90 as the ratio of the amounts by mass of solid components. When therelative amount of Component (X) is more than the above range, thesufficiently crosslinked structure cannot be obtained in the curedproduct. Moreover, it is difficult that the desired Young's modulus isobtained, and the releasing property is decreased. When the relativeamount of Component (X) is less than the above range, the Young'smodulus of the cured product is excessively great, and the cured productis hard and fragile to deteriorate the releasing property. It ispreferable that the relative amounts of Component (X) to Component (Y)is in the range of 65:35 to 10:90 and more preferably in the range of60:40 to 20:80 as the ratio of the amounts by mass of solid components.

In the heat curable resin composition, an acidic catalyst can be used asthe curing catalyst of Component (Z). The acidic catalyst is notparticularly limited, and an acidic catalyst can be suitably selectedfrom acidic catalysts conventionally known as the catalysts forcrosslinking reaction of alkyd resins. As the acidic catalyst, forexample, organic acidic catalysts such as p-toluenesulfonic acid andmethanesulfonic acid are preferable. The acidic catalyst may be usedsingly or in combination of two or more. The amount is selected, ingeneral, in the range of 0.1 to 40 parts by mass, preferably in therange of 0.5 to 30 parts by mass and more preferably in the range of 1to 20 parts by mass based on 100 parts by mass of the sum of the amountsof Component (X) and Component (Y) described above.

The heat curable resin composition is used, in general, in the form of asolution in an organic solvent due to convenience in the use. As thesolvent used in the above, a solvent can be suitably selected fromconventional solvents which exhibit solubility on Component (X) andComponent (Y) and are inert to these components. Examples of the solventinclude toluene, xylene, methanol, ethanol, isobutanol, n-butanol,acetone, methyl ethyl ketone and tetrahydrofuran. The solvent may beused singly or in combination of two or more.

The heat curable resin composition can be obtained by dissolvingComponent (X), Component (Y), Component (Z) which is used where desiredand various additive components into the organic solvent in eachspecific amount, followed by adjusting the viscosity to a value suitablefor the coating operation. The additive components used in the above arenot particularly limited and can be suitably selected from additivecomponents conventionally known as the additive components for alkydresins. Examples of the additive components include antistatic agentssuch as cationic surfactants, acrylic resins and other resins foradjusting flexibility and viscosity, leveling agents and defoamingagents.

The coating film of the resin can be formed by coating one face of thesubstrate film with the heat curable resin composition obtained asdescribed above by a conventional process such as the bar coatingprocess, the reverse roll coating process, the knife coating process,the roll knife coating process, the gravure coating process, the airdoctor coating process, the doctor blade coating process and thecapillary coating process, followed by curing the formed coated film ata temperature of about 80 to 150° C. for about several seconds toseveral minutes.

The thickness of the coating film of the resin formed as described aboveis, in general, 10 to 10,000 nm and preferably 50 to 8,000 nm asdescribed above.

(c) Formation of Coating Film of a Cured Resin Using an Active EnergyRay

When the coating film of the resin described above is a coating filmcomprising a cured product of a resin composition of the active energyray curable type, a monomer and/or an oligomer polymerizable with anactive energy ray which has two or more polymerizable unsaturated groupsin the molecule can be used as the compound of the active energy raycurable type.

The compound of the active energy ray curable type means a polymerizablecompound which can be crosslinked and cured by irradiation with a rayhaving energy quantum among electromagnetic waves and charged particles,i.e., ultraviolet light, electron beams and the like.

When the active energy ray is an active ray such as ultraviolet light,in general, a photopolymerization initiator is used in combination withthe monomer and/or the oligomer of the active energy ray curable type.When the active energy ray is electron beams, no photopolymerizationinitiator is necessary. In the present invention, it is preferable thatan active ray such as ultraviolet light is used as the active energyray. Therefore, it is preferable that the resin composition of theactive energy ray curable type is a resin composition of thephotocurable type which comprises (A) a monomer and/or an oligomer ofthe active energy ray curable type having two or more polymerizableunsaturated groups in the molecule and (B) a photopolymerizationinitiator.

Examples of the monomer of the active energy ray curable type having twoor more polymerizable unsaturated groups in the molecule used asComponent (A) in the resin composition of the photocurable type includeat least one monomer selected from (meth)acrylate compounds having afunctionality of two or greater.

Examples of the (meth)acrylate compound having a functionality of two orgreater include 1,4-butanediol di(meth)acrylate, 1,6-hexanedioldi(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycoldi(meth)acrylate, neopentyl glycol adipate di(meth)acrylate,hydroxypivalic acid neopentyl glycol di(meth)acrylate, dicyclopentanyldi(meth)acrylate, dicyclopentenyl di(meth)acrylate modified withcaprolactone, phosphoric acid di(meth)acrylate modified with ethyleneoxide, cyclohexyl di(meth)acrylate modified with ally group,isocyanurate di(meth)acrylate, trimethylolpropane tri(meth)acrylate,dipentaerythritol tri(meth)acrylate, dipentaerythritol tri(meth)acrylatemodified with propionic acid, pentaerythritol tri(meth)acrylate,trimethylolpropane tri(meth)acrylate modified with propylene oxide,tris(acryloxyethyl) isocyanurate, dipentaerythritol penta(meth)acrylatemodified with propionic acid, dipentaerythritol hexa(meth)acrylate anddipentaerythritol hexa(meth)acrylate modified with caprolactone. The(meth)acrylate compound may be used singly or in combination of two ormore.

Examples of the polymerizable oligomer of the active energy ray curabletype include polyester acrylate-based polymerizable oligomers, epoxyacrylate-based polymerizable oligomers, urethane acrylate-basedpolymerizable oligomers and polyol acrylate-based polymerizableoligomers. The polymerizable oligomers of the active energy ray curabletype may be used singly or in combination of two or more and may be usedin combination with the (meth)acrylate compounds described above.

As the photopolymerization initiator of Component (B), at least onephotopolymerization initiator can be selected as desired fromconventional photopolymerization initiators conventionally used as thephotopolymerization initiator for acrylate-based compounds. Examples ofthe photopolymerization initiator include benzoin, benzoin methyl ether,benzoin ethyl ether, benzoin isopropyl ether, benzoin n-butyl ether,benzoin isobutyl ether, acetophenone, dimethylaminoacetophenone,2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone,2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexyl phenylketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one,4-(2-hydroxyethoxy)phenyl-2-(hydroxy-2-propyl) ketone, benzophenone,p-phenylbenzophenone, 4,4′-diethylaminobenzophenone,dichlorobenzophenone, 2-methylanthraquinone, 2-ethylanthraquinone,2-tertiary-butylanthraquinone, 2-aminoanthraquinone,2-methylthioxanthone, 2-ethylthioxanthone, 2-chlorothioxanthone,2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, benzyl dimethylketal, acetophenone dimethyl ketal and p-dimethylamine benzoic acidester. The amount of the photopolymerization initiator is selected, ingeneral, in the range of 0.2 to 10 parts by mass based on 100 parts bymass of the photopolymerizable monomer and/or the photopolymerizableoligomer.

The resin composition of the active energy ray curable type, preferablythe resin composition of the photocurable type, used in the presentinvention can be prepared by dissolving or dispersing the compound ofthe active energy ray curable type and the photopolymerization initiatorwhich are described above and various additive components used wheredesired such as monofunctional active energy ray curable monomers,antioxidants, ultraviolet light absorbers, light stabilizers, levelingagents and defoaming agents in each specific amount into a suitablesolvent.

Examples of the solvent used in the above include aliphatic hydrocarbonssuch as hexane and heptane; aromatic hydrocarbons such as toluene andxylene; halogenated hydrocarbons such as methylene chloride and ethylenechloride; alcohols such as methanol, ethanol, propanol and butanol;ketones such as acetone, methyl ethyl ketone, 2-pentanone, isophoroneand cyclohexanone; esters such as ethyl acetate and butyl acetate; andcellosolve-based solvents such as ethylcellosolve.

The concentration and the viscosity of the composition prepared asdescribed above are not particularly limited as long as the coatingoperation can be conducted and can be suitably selected by thesituation.

The coating film of the resin can be formed by coating one face of thesubstrate film with the above composition by a conventional process suchas the bar coating process, the knife coating process, the roll coat gprocess, the blade coating process, the die coating process and thegravure coating process to form a coated film, followed by drying byheating where desired and, then, curing the obtained coated film byirradiation with an active energy ray.

As the active energy ray, for example, an active ray such as ultravioletlight is preferable. The ultraviolet light can be obtained from a highpressure mercury lamp, H BULB manufactured by FUSION UV SYSTEMS JAPAN K.K. or a xenon lamp. The amount of irradiation is, in general, 100 to 50mJ/cm².

The thickness of the coating film of the resin obtained as describedabove is, in general, 10 to 10,000 nm and preferably 50 to 8,000 nm asdescribed above.

The coating film for adjusting the surface film Young's modulus may bean organic film or an inorganic film. For the organic film, the resincompositions described above for the resin composition of the activeenergy ray curable type are preferable. Examples of the inorganic filminclude films of metal oxide exhibiting transparency such as indiumoxide doped with tin formed on the substrate film by the sputteringprocess or the ion plating process. The thickness of the inorganic filmis, in general, about 10 to 1,000 nm.

In the process film prepared as described above, the maximum heightroughness (Rz) of the face for forming the optical recording layer orthe barrier layer can be adjusted to 500 nm or smaller and the surfacefilm Young's modulus can be adjusted to 1.0 GPa or greater. In thepresent invention, migration of low molecular weight components in theoptical recording layer into the coating film of resin of the processfilm can be suppressed by adjusting the surface film Young's modulus at1.0 GPa or greater when the optical recording layer is formed on theface for forming the optical recording layer or the face for forming thebarrier layer of the process film, and the optical recording layerhaving Rz of 500 nm or smaller can be formed by transferring the opticalrecording layer to the pressure sensitive adhesive layer in Sheet A.

The barrier layer having Rz of 500 nm or smaller can be formed byforming the barrier layer on the face for forming the barrier layer ofthe process film and transferring the formed barrier layer to thepressure sensitive adhesive layer of Sheet B. The optical recordinglayer can be formed with excellent productivity by coating the barrierlayer with the material for forming the optical recording layer by thespin coating process, followed by drying the formed coating film. Inthis case, the coating fluid comprising the multiphoton absorbingmaterial alone can be used as the material for forming the opticalrecording layer since the spin coating process is conducted, and theoptical recording layer exhibiting excellent recording sensitivity canbe formed.

The present invention further provides a film for producing the sheetfor a multilayer optical recording medium of the present invention whichis characterized in that an optical recording layer or a barrier layeris formed on a process film on the face at the side for forming theoptical recording layer or at the side for forming the barrier layer,wherein the process film has a maximum height roughness (Rz) of 500 nmor smaller on the face at the side for forming the optical recordinglayer or at the side for forming the barrier layer. The process film,the optical recording layer, the barrier layer and the process forforming the optical recording layer and the barrier layer are the sameas those for the sheet for a multilayer recording medium describedabove.

The multilayer optical recording medium of the present invention will bedescribed in the following.

[Multilayer Optical Recording Medium]

The multilayer optical recording medium of the present invention ischaracterized in that the medium is prepared by using the sheet for amultilayer optical recording medium of the present invention, i.e.,Sheet A comprising Unit A in which an optical recording layer and apressure sensitive adhesive layer are laminated or Sheet B comprisingUnit B in which an optical recording layer, a barrier layer and apressure sensitive adhesive layer are laminated.

The number of the unit (Unit A or Unit B) in the multilayer opticalrecording medium of the present invention is riot particularly limitedand is, in general, about 2 to 200 and preferably 3 to 100. When asingle unit is used, the sufficient recording density is not obtained.When the number of the unit exceeds 200, there is the possibility thatproblems arise for writing and reading information due to absorption oflight at the layers and reflection of light at the interfaces of layers.

FIG. 8 shows a diagram exhibiting a sectional view of an example of thestructure of the multilayer optical recording medium of the presentinvention. The multilayer optical recording medium 80 has a structurehaving many adhesive layers and optical recording layers laminatedalternately on a substrate plate 9 in a manner such that an adhesivelayer 1-1, an optical recording layer 4-1, an adhesive layer 1-2, anoptical recording layer 4-2 . . . an adhesive layer 1-(n-1), opticalrecording layer 4-(n-1), an adhesive layer 1-n and an optical recordinglayer 4-n are disposed, and a protective film 12 is disposed at theuppermost layer via an adhesive layer 11, where necessary. As thesubstrate plate 9, a glass plate or a film of polycarbonate, polymethylmethacrylate or a cycloolefin resin can be used. As the protective film12, a film of a transparent resin such as polycarbonate, polymethylmethacrylate or a cycloolefin resin can be used. For the adhesive layer11, the pressure sensitive adhesive described above can be used. Themarks 6-1, 6-2, 6-(n-1) and 6-n means the first, the second, the (n-1)thand n-th Unit A, respectively.

The multilayer optical recording medium 80 having the structuredescribed above can be produced, for example, as described in thefollowing using Sheet A 40 for a multilayer optical recording layershown in FIG. 4.

The first release film 2 is peeled from Sheet A 40, and the pressuresensitive adhesive layer 1-1 is exposed. The substrate plate 9 and SheetA are laminated in a manner such that the exposed pressure sensitiveadhesive layer 1-1 and the substrate plate 9 face each other. Theprocess film 5 is peeled from the resultant laminate, and the opticalrecording layer 4-2 is exposed. The first release film 2 is peeled fromanother Sheet A for a multilayer optical recording medium 40 to expose apressure sensitive adhesive layer 1-1. The laminate obtained above andthe other Sheet A 40 are laminated in a manner such that the opticalrecording layer 4-2 and the pressure sensitive adhesive layer 1-1exposed above (forming 1-3 in FIG. 8, not shown in the figure) face eachother. A multilayer laminating structure in which n layers each of theoptical recording layer and the pressure sensitive adhesive layer arelaminated can be obtained by repeating the lamination by the sameprocedures. The multilayer optical recording medium 80 can be obtainedby attaching the protective film 12 having an adhesive layer 11 at theuppermost layer of the multilayer laminate structure.

FIG. 9 shows a diagram exhibiting a sectional view of another example ofthe structure of the multilayer optical recording medium of the presentinvention. The multilayer optical recording medium 90 has a structurehaving many Unit B, in which a pressure sensitive adhesive layer, abarrier layer and an optical recording layer are laminated in thisorder, laminated on a substrate plate 9 in a manner such that a pressuresensitive adhesive layer 1-1, a barrier layer 7-1, an optical recordinglayer 4 a-1, a pressure sensitive adhesive layer 1-2, a barrier layer7-2, an optical recording layer 4 a-2 . . . a pressure sensitiveadhesive layer 1-(n-1), a barrier layer 7-(n-1), an optical recordinglayer 4-(n-1), a pressure sensitive adhesive layer 1-n, a barrier layer7-n and an optical recording layer 4-n are disposed, and a protectivefilm 12 is disposed at the uppermost layer via an adhesive layer 11,where necessary. For the substrate plate 9, the protective film 12 andthe adhesive layer 11, the same films and layers as those describedabove can be used. The marks 8-1, 8-2, 8-(n-1) and 8-n means the first,the second, the (n-1)th and n-th Unit B, respectively.

The multilayer optical recording medium 90 having the structuredescribed above can be produced, for example, as described in thefollowing using Sheet B 70 for a multilayer optical recording layershown in FIG. 7.

The first release film 2 is peeled from Sheet B 70, and the pressuresensitive adhesive layer 1-1 is exposed. The substrate plate 9 and SheetB are laminated in a manner such that the exposed pressure sensitiveadhesive layer 1-1 and the substrate plate 9 face each other. The firstrelease film 2 is peeled from another Sheet B for a multilayer opticalrecording medium 70 to expose a pressure sensitive adhesive layer 1-1.The laminate obtained above and the other Sheet B 70 are laminated in amanner such that the optical recording layer 4 a-2 of the above laminateand the pressure sensitive adhesive layer 1-1 exposed above (forming 1-3in FIG. 8, not shown in the figure) face each other. A multilayerlaminating structure in which n layers each of the optical recordinglayer, the barrier layer and the pressure sensitive adhesive layer arelaminated can be obtained by repeating the lamination by the sameprocedures. The multilayer optical recording medium 90 shown in FIG. 9can be obtained by attaching the protective film 12 having an adhesivelayer 11 to the optical recording layer 4 a-n at the uppermost layer ofthe multilayer structure.

The multilayer optical recording medium of the present inventionobtained as described above may further comprise reflection layers,layers of dielectric substances, protective layers and layers havingrecording pits and groove patterns in combination with the opticalrecording layer, the adhesive layer and the barrier layer, wherenecessary.

EXAMPLES

The present invention will be described more specifically with referenceto examples in the following. However, the present invention is notlimited to the examples.

Properties in Examples and Comparative Examples were obtained by thefollowing methods.

(1) Measurement of the Maximum Height Roughness (Rz)

A laminate film having the structure shown in FIG. 3 in which a processfilm, an optical recording layer (the thickness: 0.6 μm) or a barrierlayer (the thickness: 1.0 μm), a pressure sensitive adhesive layer (thethickness: 10 μm) and a release film were laminated in this order wasprepared. The maximum height roughness (Rz) of the face for forming theoptical recording layer or the face for forming the barrier layer of theprocess film used for the laminate film was measured. The process filmin the laminate film was peeled, and Rz of the exposed optical recordinglayer or barrier layer (Example 7) was also measured,

Rz was measured using a surface roughness meter [manufactured byMITUTOYO Corporation; the name of the instrument: “SV-3,000”]

(2) Measurement of the Surface Film Young's Modulus of a Process Film

The surface film Young's modulus of each process film on the face forforming the optical recording layer or the face for forming the barrierlayer was measured using a nanoindenter [manufactured by MTS Company;the name of the instrument: “NANOINDENTER TEST WORKS-4”] which was aninstrument for measuring mechanical properties of a thin film. The valueat the position of 50 nm in the direction of the thickness was used.

(3) Measurement of the Haze Value

A laminate film having the same structure as that described above in (1)was prepared. The release film was peeled, and the laminate film wasattached to a slide glass as the support in a manner such that theexposed pressure sensitive adhesive layer faced the slide glass. Then,after the process film was peeled, incident light was applied at theside of the optical recording layer or the barrier layer, and the hazevalue was measured using a haze meter [manufactured by NIPPON DENSHOKUINDUSTRIES Co., Ltd.; the name of the instrument: “NDH2000”]. When thehaze value was 2.5% or smaller, the sample was regarded to have passedthe test.

(4) Measurement of the Number of Bright Spots

A laminate film having the same structure as that described above in (1)was prepared. The release film was peeled, and the laminate film wasattached to a slide glass as the support in a manner such that theexposed pressure sensitive adhesive layer faced the slide glass. Afterthe process film was peeled, the face at the side of the opticalrecording layer or the barrier layer was observed by a digitalmicroscope [manufactured by KEYENS Corporation; the name of theinstrument: “VHX-200”] at a magnification of 1,000. The number of brightspots in the area of 100 μm×100 μm was counted. The bright spot isderived from roughness of the optical recording layer or the barrierlayer. When the number of bright spots was 50/10⁴ μm², the sample wasregarded to have passed the test.

(5) Migration of Low Molecular Weight Components into a Process Film(the Fraction of Residual Components)

In Examples 1 to 6 and Comparative Example 1, a laminate film having thesame structure as that described above in (1) was prepared. The releasefilm was peeled, and the laminate film was attached to a slide glass asthe support in a manner such that the exposed pressure sensitiveadhesive layer faced the slide glass. After the process film was peeled,the absorption of light with the peeled process film was measured, anda-value (%) was obtained by the following equation:a={[absorption with process film after peeling the recording layer(absorption λ_(max))]/[absorption with process film having recordinglayer (absorption λ_(max))]}×100

When the a-value was 10% or smaller, migration of low molecular weightcomponents derived from the optical recording layer to the process filmwas absent and, when the a-value exceeded 10%, migration of lowmolecular weight components to the process film was present. Themeasurement was conducted at a wavelength of 200 to 800 nm.

(6) Measurement of Peeling Force

A laminate film having the same structure as that described above in (1)was prepared. After the release film was peeled, the laminate film wasattached to a glass substrate in a manner such that the exposed pressuresensitive adhesive layer faced the glass substrate. Then, the 180°peeling test of the process film was conducted at 25° C. by the methodof Japanese Industrial Standard Z 0327, and the peeling force wasmeasured.

(7) Measurement of Contact Angle

The contact angle of a liquid droplet on the face of a process film wasmeasured by the liquid droplet method using a contact angle meter[manufactured by KYOWA INTERFACE SCIENCE Co., Ltd.; the type “CA-D”]. Adroplet of purified water (the diameter: 2 mm) was used as the liquiddroplet.

(8) Observation of Repelling of a Coating Fluid

The presence or the absence of repelling of a coating fluid was visuallyobserved immediately after a coating fluid for an optical recordinglayer was applied to the process film in Examples 1 to 6 and ComparativeExamples 1 and 2 and immediately after a coating fluid for forming abarrier layer was applied to the process film in Example 7.

Preparation Example 1

Preparation of Coating Fluid (a) for Forming an Optical Recording Layer

A diarylethene [manufactured by TOKYO CHEMICAL INDUSTRY Co., Ltd.; thenumber-average molecular weight: 326] as the two-photon absorbingmaterial and polymethyl methacrylate [manufactured by SIGMA-ALDRICHJAPAN Company; the weight-average molecular weight: 350,000] as thematrix material were mixed in amounts such that the ratio of the amountsby mass was 1:9. Methyl ethyl ketone as the solvent was added, andCoating fluid (a) for forming an optical recording layer having aconcentration of solid components of 5% by mass was prepared.

Preparation Example 2

Preparation of Coating Fluid (b) for Forming a Barrier Layer

Polyvinyl alcohol [manufactured by THE NIPPON SYNTHETIC CHEMICALINDUSTRY Co., Ltd.; the trade name: “GOSENOL EG-05”] was dissolved intopurified water as the solvent, and Coating fluid (b) for forming abarrier layer having a concentration of solid components of 5% by masswas prepared.

Preparation Example 3

Preparation of a Pressure Sensitive Adhesive Sheet

(1) Preparation of Coating Fluid (c) of a Pressure Sensitive Adhesive

To 100 parts by mass of an ethyl acetate solution (the concentration ofsolid components: 30% by mass) of an acrylic acid ester copolymer (theweight-average molecular weight: 500,000) obtained by using 96 parts bymass of n-butyl acrylate and 4 parts by mass of acrylic acid, 8 parts bymass of an aluminum chelate-based crosslinking agent [manufactured bySOKEN CHEMICAL AND ENGINEERING Co., Ltd.; the trade name: “M-5A”; theconcentration of solid components: 5% by mass] was added. The resultantmixture was stirred until a uniform solution was obtained, and Coatingfluid (c) of a pressure sensitive adhesive was prepared.

(2) Preparation of the First Release Film

The smooth face (Rz: 80 nm) of a polyethylene terephthalate film havinga thickness of 50 μm [manufactured by TOYOBO Co., Ltd.; the trade name:“A4100”] was coated, using a Mayer bar #4, with a coating fluid whichwas obtained by adding 1.5 part by mass of a catalyst [manufactured bySHIN-ETSU CHEMICAL Co., Ltd.; the trade name: “CAT-PL-50T”] to 100 partsby mass of a silicone resin [manufactured by SHIN-ETSU KAGAKU Co., Ltd,;the trade name: “KS-847H”], followed by adding toluene to dilute thefluid so that the concentration of solid components was L3% by mass. Theformed coating film was dried at 150° C. for 1 minute to form a siliconerelease layer having a thickness of 100 nm, and the first release filmwas prepared.

(3) Preparation of the Second Release Film

The smooth face (Rz: 80 nm) of a polyethylene terephthalate film havinga thickness of 50 μm [manufactured by TOYOBO Co., Ltd.; the trade name:“A4100”] was coated, using a Mayer bar #4, with a coating fluid whichwas obtained by adding 1.0 part by mass of a catalyst [manufactured bySHIN-ETSU CHEMICAL Co., Ltd.; the trade name: “CAT-PL-50T”] to 100 partsby mass of a silicone resin [manufactured by SHIN-ETSU CHEMICAL Co.,Ltd.; the trade name: “KS-835”, ]followed by adding toluene to dilutethe fluid so that the concentration of solid components was 1.3% bymass. The formed coating film was dried at 150° C. for 1 minute to forma silicone release layer having a thickness of 100 nm, and the secondrelease film was prepared.

(4) Preparation of a Pressure Sensitive Adhesive Sheet

The face of the first release film obtained above in (2) at the sidehaving the silicone release layer was coated with Coating fluid (c) of apressure sensitive adhesive obtained above in (1) by the knife coatingprocess. After the formed coating film was dried at 90° C. for 1 minute,the face having the silicone release layer of the second release filmobtained above in (3) was laminated to the firmed coating layer, and asheet of a pressure sensitive adhesive was prepared. The thickness ofthe pressure sensitive adhesive layer was 10 μm.

Example 1

The smooth face (Rz of the face containing no fillers: 80 nm; thesurface film Young's modulus: 3.46 GPa) of a polyethylene terephthalatefilm having a thickness of 50 μm [manufactured by TOYOBO Co., Ltd.; thetrade name: “A4100”] (hereinafter, referred to as Process film [1]) wascoated with Coating fluid (a) for forming an optical recording layer bythe gravure coating process. The formed coated film was dried at 90° C.for 1 minute, and an optical recording layer having a process film wasprepared as the film for producing a sheet for a multilayer opticalrecording medium. The thickness of the optical recording layer was 0.6μm.

Then, the second release film of the pressure sensitive adhesive sheetwas peeled. The exposed face of the pressure sensitive adhesive layer inthe pressure sensitive adhesive sheet was laminated to the face of theoptical recording layer having a process film at the side of the opticalrecording layer, and a sheet for a multilayer optical recording mediumwas prepared. The properties of the obtained sheet for a multilayeroptical recording medium are shown in Table 1.

Example 2

(1) Preparation of Process Film [2]

The smooth face of a polyethylene terephthalate film having a thicknessof 50 μm [manufactured by TOYOBO Co., Ltd.; the trade name: “A4100”] wascoated, using a Mayer bar #4, with coating fluid of a heat curable alkydresin which was obtained by mixing 3 parts by mass of p-toluenesulfonicacid as the catalyst to 100 parts by mass of an alkyd resin[manufactured by HITACHI KASEI POLYMER Co., Ltd.; the trade name:“TESFINE 303”; the concentration of solid components: 20% by mass]. Theformed coating film was dried and cured by heating at 140° C. for 1minute to form a layer of a heat cured resin having a thickness of 100nm, and Process film [2] was prepared.

Rz of the face of the layer of a heat cured resin (the face for formingan optical recording layer) of Process film [2] was 70 nm, and thesurface film Young's modulus of the coating film of the resin was 3.68GPa.

(2) Preparation of a Sheet for a Multilayer Optical Recording Medium

A sheet for a multilayer optical recording medium was prepared by thesame procedures as those conducted in Example 1 except that, in place ofProcess film [1, ]Process film [2] obtained above in (1) was coated withCoating fluid (a) for forming an optical recording layer. The propertiesof the obtained sheet for a multilayer optical recording medium areshown in Table 1.

Example 3

(1) Preparation of a Fluid of a Butadiene-Based Releasing Agent

1,4-Polybutadiene rubber [manufactured by ZEON Corporation; the tradename: “NIPOL 1241”; the content of the cis-1,4-bond: 35%] was dilutedwith toluene, and a dispersion having a concentration of solidcomponents of 0.5% by mass was prepared. Then, an antioxidant[manufactured by CIBA SPECIALTY CHEMICALS K. K.; the trade name:“IRGANOX HP2251”] was added to the dispersion in an amount of 1 part bymass based on 100 parts by mass of the 1,4-polybutadiene rubber in thedispersion, and a fluid of a butadiene-based releasing agent wasprepared.

(2) Preparation of Process Film [3]

The smooth face (Rz of the face containing no fillers: 210 nm) of apolyethylene terephthalate film having a thickness of 38 μm[manufactured by MITSUBISHI POLYESTER FILM Corporation; the trade name:“PET38 T-700”] was coated with the fluid of a butadiene-based releasingagent obtained above in (1) using a Mayer bar #4, and the formed coatedfilm was dried by heating at 100° C. for 1 minute. The dried coated filmwas irradiated with ultraviolet light of 1,320 mJ/cm² to form a layer ofa butadiene-based releasing agent having a thickness of 200 nm, andProcess film [3] was prepared.

Rz of the face treated for releasing (the face for forming an opticalrecording layer) of Process film [3] was 210 nm, and the surface filmYoung's modulus was 142 GPa.

(3) Preparation of a Sheet for a Multilayer Optical Recording Medium

A sheet for a multilayer optical recording medium was prepared by thesame procedures as those conducted in Example 1 except that, in place ofProcess film [1, ]Process film [3] obtained above in (2) was coated withCoating fluid (a) for forming an optical recording layer. The propertiesof the obtained sheet for a multilayer optical recording medium areshown in Table 1.

Example 4

A sheet for a multilayer optical recording medium was prepared by thesame procedures as those conducted in Example 1 except that acycloolefin resin film having a thickness of 100 μm [manufactured byZEON Corporation; the trade name: “ZF16”] (hereinafter, referred to asProcess film [4]) was used in place of Process film [1, ]and the face(Rz: 50 nm; the surface film Young's modulus: 2.61 GPa) exposed bypeeling the protective film of the film was coated with Coating fluid(a) for forming an optical recording layer. The properties of theobtained sheet for a multilayer optical recording medium are shown inTable 1.

Example 5

(1) Preparation of a Dispersion of a Resin of the Photocurable Type

A dispersion of a resin of the photocurable type having a concentrationof solid components of 38.6% by mass was prepared by adding 1.6 parts bymass of a photopolymerization initiator [manufactured by CIBA SPECIALTYCHEMICALS K. K.; the trade name: “IRGACURE 907”] to 100 parts by mass ofa resin of the ultraviolet light curable type [manufactured by NIPPONKAYAKU Co., Ltd.; “KAYANOVA FOP-5000B”; the content of solid components:80%], followed by diluting the obtained mixture with toluene and methylethyl ketone.

(2) Preparation of Process Film [5]

A polyethylene terephthalate film having a thickness of 38 μm[manufactured by MITSUBISHI POLYESTER FILM Corporation; the trade name:“PET38 T-300”] (Rz: 305 nm) was coated with the dispersion of a resin ofthe photocurable type obtained above in (1) by the gravure coatingprocess, and the formed coated film was dried by heating at 90° C. for 1minute. The formed coated film was irradiated with ultraviolet light of500 mJ/cm² to form a photocured resin layer having a thickness of 5 μm,and Process film [5] was prepared.

Rz of the face of the photocured resin (the face for forming an opticalrecording layer) of Process film [5] was 10 nm, and the surface filmYoung's modulus was 10.80 GPa.

(3) Preparation of a Sheet for a Multilayer Optical Recording Medium

A sheet for a multilayer optical recording medium was prepared by thesame procedures as those conducted in Example 1 except that Process film[5] obtained above in (2) was used in place of Process film [1, ]and theface of the photocured resin was coated with Coating fluid (a) forforming an optical recording layer. The properties of the obtained sheetfor a multilayer optical recording medium are shown in Table 1.

Example 6

(1) Preparation of Process Film [6]

Process film [6] was prepared by forming a film of indium oxide dopedwith tin (ITO) having a thickness of 150 nm on a polyethylenenaphthalate film having a thickness of 200 μm [manufactured by TEIJINCHEMICALS Ltd.; the trade name: “TEONEX Q65FA”] (Rz: 92 nm).

Rz of the face of the ITO film (the face for forming an opticalrecording layer) of Process film [6] was 90 nm, and the surface filmYoung's modulus was 13.00 GPa.

(2) Preparation of a Sheet for a Multilayer Optical Recording Medium

A sheet for a multilayer optical recording medium was prepared by thesame procedures as those conducted in Example 1 except that Process film[6] obtained above in (1) was used in place of Process film [1], and theface of the ITO film was coated with Coating fluid (a) for forming anoptical recording layer. The properties of the obtained sheet for amultilayer optical recording medium are shown in Table 1.

Example 7

(1) Preparation of a Barrier Layer having a Process Film

The smooth face of Process film [1] was coated with Coating fluid (b)for forming a barrier layer by the gravure coating process. The formedcoating film was dried at 100° C. for 1 minute, and a barrier layerhaving a process film as the film for producing a sheet for a multilayeroptical recording medium was prepared. The thickness of the barrierlayer was 1.0 μm.

(2) Preparation of a Sheet for a Multilayer Optical Recording Medium

The second release film in the pressure sensitive adhesive sheet waspeeled. The exposed face of the pressure sensitive adhesive waslaminated to the barrier layer having a process film obtained above in(1), and a laminate film was prepared. The barrier layer exposed bypeeling the process film was coated with Coating fluid (d) for formingan optical recording layer having a concentration of solid components of5% by mass which was obtained by dissolving a diarylethene [Manufacturedby TOKYO CHEMICAL INDUSTRY Co., Ltd.] as the two-photon absorbingmaterial into methyl isobutyl ketone as the solvent by the spin coatingprocess. The formed coated film was dried at 90° C. for 1 minute to forman optical recording layer having a thickness of 0.6 μm, and a sheet forproducing an optical recording medium was prepared. The surface heightroughness Rz of the optical recording layer was 53 nm. The properties ofthe obtained sheet for a multilayer optical recording medium are shownin Table 1.

Comparative Example 1

(1) Preparation of a Fluid of a Butadiene-Based Releasing Agent

1,4-Polybutadiene rubber [manufactured by ZEON Corporation; the tradename: “NIPOL 1241”; the content of the cis-1,4-bond: 35%] was dilutedwith toluene, and a dispersion having a concentration of solidcomponents of 0.5% by mass was prepared. Then, an antioxidant[manufactured by CIBA SPECIALTY CHEMICALS K. K.; the trade name:“IRGANOX HP2251”] was added to the dispersion in an amount of 1 part bymass based on 100 parts by mass of the 1,4-polybutadiene rubber in thedispersion, and a fluid of a butadiene-based releasing agent wasprepared.

(2) Preparation of Process Film [7]

A polyethylene terephthalate film having a thickness of 38 μm[manufactured by MITSUBISHI POLYESTER FILM Corporation; the trade name:“PET38 T-100”] was coated with the fluid of a butadiene-based releasingagent obtained above in (1) using a Mayer bar #4, and the formed coatedfilm was dried by heating at 100° C. for 1 minute. A layer of abutadiene-based releasing agent having a thickness of 50 nm was formedby irradiation with ultraviolet light of 110 mJ/cm², and Process film[7] was prepared.

Rz of the face treated for releasing of Process film [7] was 987 nm, andthe surface film Young's modulus was 0.32 GPa.

(3) Preparation of a Sheet for a Multilayer Optical Recording Medium

A sheet for a multilayer optical recording medium was prepared by thesame procedures as those conducted in Example 1 except that Process film[7] obtained above in (2) was used in place of Process film [1, ]andCoating fluid (a) for forming an optical recording layer was applied.The properties of the obtained sheet for a multilayer optical recordingmedium are shown in Table 1,

Comparative Example 2

(1) Preparation of a Silicone-Based Releasing Agent

To 85 parts by mass of a silicone-based releasing agent [manufactured byDOW CORNING TORAY Co., Ltd.; the trade name: “BY24-510”], 2 parts bymass of a catalyst [manufactured by DOW CORNING TORAY Co., Ltd.; thetrade name: “BY24-835”] and 2,400 parts by mass of toluene were added,and a fluid of a silicone-based releasing agent (the concentration: 1.2%by mass) was prepared.

(2) Preparation of Process Film [8]

A polyethylene terephthalate film having a thickness of 38 μm[manufactured by MITSUBISHI POLYESTER FILM Corporation; the trade name:“PET38 T-100”] was coated with the fluid of a silicone-based releasingagent obtained above in (1). The formed coated film was dried by heatingat 120° C. for 1 minute to form a layer of a silicone-based releasingagent having a thickness of 80 nm, and Process film [8] was prepared. Rzof the face treated for releasing of Process film [8] was 1,090 nm, andthe surface film Young's modulus was 0.19 GPa.

(3) Preparation of a Sheet for a Multilayer Optical Recording Medium

Preparation of a sheet for a multilayer optical recording medium wasattempted by the same procedures as those conducted in Example 1 exceptthat Process film [8] was used in place of Process film [1]. The coatingfluid was markedly repelled, and no optical recording layer could beformed.

TABLE 1 Maximum height roughness Process film [Rz] maximum surface ofoptical height film recording roughness Young's layer Haze [Rz] modulusor barrier value (nm) (GPa) layer (nm) (%) Example 1 80 3.46 85 1.1Example 2 90 3.68 78 1.0 Example 3 210 1.42 205 2.0 Example 4 50 2.61 521.0 Example 5 10 10.80 17 1.1 Example 6 90 13.00 92 1.4 Example 7 803.46 87 0.9 Comparative 987 0.32 804 4.0 Example 1 Comparative 1090 0.19— * Example 2 Num- ber Fraction of of bright residual Peeling spotscompo- strength Contact (/10⁴ nents (mN/25 angle Repel- μm²) (%) cm)(degree) ling Example 1 1 0.0 100 70 absent Example 2 2 4.0 78 76 absentExample 3 32 7.0 52 95 absent Example 4 4 0.0 80 85 absent Example 5 40.0 84 74 absent Example 6 10 0.0 175 32 absent Example 7 1 — 102 70absent Comparative 63 19.0 800 101 present Example 1 Comparative — * 109present Example 2 * Formation of an optical recording layer could not beachieved.

As shown in Table 1, in Examples 1 to 7, the haze value was smaller andthe number of the bright spots was smaller than those in ComparativeExample 1, and the results in Examples 1 to 7 passed the test. Thefraction of residual components was small, i.e., smaller than 10%, andthe peeling strength was smaller than that in Comparative Example 1. InExamples 1 to 7, the contact angle on the surface of the process filmwas 70 to 95 degrees, and repelling of the coating fluid was absent. InComparative Example 1, repelling of the coating fluid was present, andRz of the obtained optical recording layer was great. The process filmof Comparative Example 2 showed marked repelling of the coating fluid,and the formation of an optical recording layer could not be achieved.

Industrial Applicability

The sheet for a multilayer optical recording medium of the presentinvention enables to produce a multilayer optical recording mediumhaving a repeating structure in which a plurality of optical recordinglayers are laminated with excellent precision and quality.

The invention claimed is:
 1. A sheet for a multilayer optical recordingmedium having a repeating structure comprising a plurality of laminatedoptical recording layers, wherein the sheet has a structure comprising aunit in which an optical recording layer and an adhesive layer arelaminated or a structure comprising a unit in which an optical recordinglayer, a barrier layer and an adhesive layer are laminated in thisorder, and a maximum height roughness (Rz) of the optical recordinglayer or the barrier layer is 500 nm or smaller.
 2. The sheet for amultilayer optical recording medium according to claim 1, wherein, inthe sheet having a structure comprising a unit in which an opticalrecording layer and an adhesive layer are laminated, the opticalrecording layer is formed by transfer of an optical recording layerformed on a process film on a face at a side for forming the opticalrecording layer, the face at the side for forming the optical recordinglayer of the process film having a maximum height roughness (Rz) of 500nm or smaller.
 3. The sheet for a multilayer optical recording mediumaccording to claim 1, wherein, in the sheet having a structurecomprising a unit in which an optical recording layer, a barrier layerand an adhesive layer are laminated, the barrier layer is formed bytransfer of a barrier layer formed on a process film on a face at a sidefor forming the barrier layer, the face at the side for forming thebarrier layer of the process film having a maximum height roughness (Rz)of 500 nm or smaller.
 4. The sheet for a multilayer optical recordingmedium according to claim 2, wherein surface film Young's modulus on theface of the process film at the side for forming the optical recordinglayer or at the side for forming the barrier layer is 1.0 GPa orgreater.
 5. The sheet for a multilayer optical recording mediumaccording to claim 2, wherein the face of the process film at the sidefor forming the optical recording layer or at the side for forming thebarrier layer comprises no fillers.
 6. The sheet for a multilayeroptical recording medium according to claim 2, wherein the process filmcomprises a substrate film and a coating film disposed on the substratefilm, and the coating film has a thickness of 80 to 10,000 nm and isdisposed on the face of the process film at the side for forming theoptical recording layer or at the side for forming the barrier layer tosuppress roughness of the substrate.
 7. The sheet for a multilayeroptical recording medium according to claim 2, wherein the face of theprocess film at the side for forming the optical recording layer or atthe side for forming the barrier layer comprises a coating filmcomprising a polyester-based resin or a resin cured with an activeenergy ray.
 8. The sheet for a multilayer optical recording mediumaccording to claim 1, wherein the optical recording layer is a layercomprising a multiphoton absorbing material.
 9. A multilayer opticalrecording medium prepared by using the sheet according to claims
 1. 10.The sheet for a multilayer optical recording medium according to claim3, wherein surface film Young's modulus on the face of the process filmat the side for forming the optical recording layer or at the side forforming the barrier layer is 1.0 GPa or greater.
 11. The sheet for amultilayer optical recording medium according to claim 3, wherein theprocess film comprises a substrate film and a coating film disposed onthe substrate film, and the coating film has d thickness of 80 to 10,000nm and is disposed on the face of the process film at the side forforming the optical recording layer or at the side for forming thebarrier layer to suppress roughness of the substrate.
 12. The sheet fora mutilayer optical recording medium according to claim 4, wherein theprocess film comprises a substrate film and a coating film disposed onthe substrate film, and the coating film has a thickness of 80 to 10,000nm and is disposed on the face of the process film at the side forforming the optical recording layer or at the side for forming thebarrier layer to suppress roughness of the substrate.
 13. The sheet fora multilayer optical recording medium according to claim 5, wherein theprocess film comprises a substrate film and a coating film disposed onthe substrate film, and the coating film has a thickness of 80 to 10,000nm and is disposed on the face of the process film at the side forforming the optical recording layer or at the side for forming thebarrier layer to suppress roughness of the substrate.
 14. The sheet fora multilayer optical recording medium according to claim 3, wherein theface of the process film at the side for forming the optical recordinglayer or at the side for forming the barrier layer comprises a coatingfilm comprising a polyester-based resin or a resin cured with an activeenergy ray.
 15. The sheet for a multilayer optical recording mediumaccording to claim 4, wherein the face of the process film at the sidefor forming the optical recording layer or at the side for forming thebarrier layer comprises a coating film comprising a polyester-basedresin or a resin cured with an active energy ray.
 16. The sheet for amultilayer optical recording medium according to claim 5, wherein theface of the process film at the side for forming the optical recordinglayer or at the side for forming the barrier layer comprises a coatingfilm comprising a polyester-based resin or a resin cured with an activeenergy ray.
 17. The sheet for a multilayer optical recording mediumaccording to claim 6, wherein the face of the process film at the sidefor forming the optical recording layer or at the side for forming thebarrier layer comprises a coating film comprising a polyester-basedresin or a resin cured with an active energy ray.